President signs treaty to reduce nuclear weapons

President Obama is in Prague today, where he signed the START Treaty along with Russian President Dmitry Medvedev. The treaty will reduce the number of nuclear warheads between the two countries by almost 40 percent, from 2,700 to 1,550.

We have a live update from David Sanger, chief White House correspondent for The New York Times, who is in Prague and witnessed the historic signing.

Also with us is Will Tobey, Senior Fellow at the Belfer Center for Science and International Affairs at the John F. Kennedy School of Government at Harvard University. Tobey was the former deputy administrator of the National Nuclear Security Administration from 2006 to 2009. He believes the treaty is a modest improvement from the current state of affairs, but also says that as you lower the number of nuclear weapons in the world, the threat to stability actually increases.